The present invention relates to an exposure apparatus or system and method using an electron beam. The exposure of a subject using an electron beam as contemplated by the present invention can be employed for forming patterns in an electronic memory device such as magnetic bubble device by irradiating with the electron beam.
In effecting the exposure using the radiation from an electron beam to form a chevron figure in a magnetic bubble memory device, it is accepted practice to approximate the chevron figure P by many rectangular picture elements e.sub.1, e.sub.2, . . . , e.sub.n as shown in FIG. 1, to store the data for the individual rectangular picture elements in a main memory, and to successively read the data from the main memory to supply generating instructions to a device for irradiating the electron beam. This method requires a digital-to-analog converter for converting the digital data for each of the rectangular picture elements into irradiation instruction signals having analog quantities.
However, since there exist a great number of rectangular picture elements, the above-mentioned conventional method presented a problem with regard an enormous amount of data that must be transferred from the main memory to the device for generating the electron beam responsive to instruction from the central processor. Another problem existed with regard to the difficulty in increasing the operation speed since large settling times were necessary for the digital-to-analog converter. When the magnetic bubble memory device employs: a figure consisting of a chevron set in which a great number of chevron figures of the same pattern are arrayed; as well as a digital-to-analog converter consisting of a digital-to-analog converter for start-point data which determines the starting point for each rectangular picture element for each chevron figure, and a digital-to-analog converter for converting data for scanning each rectangular picture element for each chevron figure, the start-point of the rectangular picture elements for the chevron figures must be determined many times. That is, the digital-to-analog converter needs a longer settling time.
FIG. 2 illustrates another conventional exposure system using an electron beam. According to this method, a desired figure P is successively scanned along horizontal lines, and a start point a and an end point b are specified for each line. Even in this system which has many startpoints, the digital-to-analog converter requires an increased setting time for each of the start-points, and makes it difficult to increase the operation speed. This system has been disclosed, for example, in A. M. Patlach et al: Electron-beam Lithographic Pattern Generation System, J. Vac. Sci. Technol. 15(3), American Vacuum Society, May/June, 1978.
The present invention is proposed to solve the above-mentioned problems inherent in the conventional exposure systems or apparatus and methods using an electron beam.